[논문]탄소섬유강화 플라스틱(CFRP)로 보강된 원형콘크리트 교각의 지진성능 평가

마벨; 박종섭

doi:10.12652/ksce.2020.40.2.0197

탄소섬유강화 플라스틱(CFRP)로 보강된 원형콘크리트 교각의 지진성능 평가
Seismic Performance of Circular Concrete Bridge Piers Externally Strengthened by Carbon Fiber Reinforced Polymer 원문보기

대한토목학회논문집 = Journal of the Korean Society of Civil Engineers, v.40 no.2, 2020년, pp.197 - 208

마벨 (상명대학교 건설시스템공학과) , 박종섭 (상명대학교 건설시스템공학과)

초록
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본 연구에서는 콘크리트 원형 교각의 동적거동 특성을 향상시키기 위하여 최적의 탄소섬유강화 플라스틱 설치 방법에 대해서 해석적 기법을 적용하여 평가하였다. 범용구조해석 프로그램인 ABAQUS가 해석연구에 사용되었으며, 소성 및 손상 콘크리트 재료특성을 적용하여 구조물의 비선형해석을 실시하였다. CFRP 적용에 따른 내진성능 향상도를 분석하고자 교각높이와 보강된 높이 비율, 교각 지름 대비 CFRP 보강 두께를 해석변수로 고려하여 거동특성과 연성도를 비교 분석하였다. 해석결과를 토대로 보강에 따른 정량적인 성능향상을 확인할 수 있었으며, 보강 재료 두께 증가보다는 교각높이 대비 보강높이 비율이 보다 성능에 큰 영향을 미치는 것을 알 수 있었다.

Abstract ▼ AI-Helper

This paper evaluated the optimum Carbon Fiber Reinforced Polymer (CFRP) using a circular concrete bridge pier subjected to dynamic loading. A three-dimensional finite element model was simulated using finite element program, ABAQUS. Concrete Damage Plasticity (CDP) option and plastic properties of the materials were incorporated to model the non-linearity of the structure. The analyses parameters were changed in length-to-height ratio and width-to-span ratio where columns were subjected to dynamic loading. Numerical analysis was conducted, and the seismic performance of the structures were evaluated by analyzing the ductility behavior of the structure. Results showed that the use of CFRP enhances the structural performance of column and revealed that the increase in length-to-height ratio plays vital role of improving the performance of the structure than the change in width-to-span ratio.

주제어

표/그림 (25)

그림 Fig. 1. Energy Index
그림 Fig. 2. Nomenclature of Parametric Models
그림 Fig. 3. Model Configuration Setup
표 Table 1. Nomenclature of Length-to-Height Ratio Cases
표 Table 2. Nomenclature of Width-to-Span Ratio Cases
그림 Fig. 4. Boundary and Loading Conditions of Meshed Numerical Model
표 Table 4. Material Properties of Concrete
표 Table 3. Material Properties of CFRP
그림 Fig. 5. Applied Dynamic Loading
그림 Fig. 6. Stress-Strain Curve of Simulated Concrete
그림 Fig. 7. Evident Deformation at Plastic Hinge Region
그림 Fig. 8. Comparison of Stress-Strain Curve without CFRP to Structure with CFRP
그림 Fig. 9. Load-Deflection Curve of Concrete Column without CFRP
그림 Fig. 10. Individual Load-Deflection Hysteresis Curve and Skeleton Curve with Varying Length-to-Height Ratio
표 Table 5. Comparison of Stress according to CFRP Ratio
그림 Fig. 11. Individual Load-Deflection Hysteresis Curve and Skeleton Curve with Varying Width-to-Span Ratio
그림 Fig. 12. Comparison of Load-Deflection Hysteresis Curve with and without CFRP
그림 Fig. 13. Comparison of Load-Deflection Skeleton Curve with and without CFRP
그림 Fig. 14. Effect of Increasing Length-to-Height Ratio to the Performance of the Structure
표 Table 6. Comparison of Base Shear according to CFRP Ratio
표 Table 7. Comparison of Displacement according to CFRP Ratio
표 Table 8. Comparison of Ductility according to CFRP Ratio
그림 Fig. 15. Effect of Increasing Width-to-Span Ratio to the Performance of the Structure
표 Table 9. Performance of the Structure according to Change in Length-to-Height Ratio
표 Table 10. Performance of the Structure according to Change in Width-to-Span Ratio

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문제 정의

The following conclusions are drawn based by means of the results of the conducted finite element analysis. The main aim of this paper was to optimize the application of CFRP. The performance of a circular concrete column was analyzed according to the of change in length-to-height ratio and width-to-span ratio of CFRP.
After years of study using FRP bars and straps as retrofit materials, Toutanji (1999) extended the study to FRP sheets and presented a structural model for the behavior of GFRP and CFRP confined concrete columns using large-scale samples in experiments. The researches presented that the use of FRP as a material for retrofit provided desirable results in increasing the performance of the structure.

가설 설정

as the ultimate load. The inelastic, elastic and total energies were calculated through numerical integration and in this paper, the ratio of inelastic energy to total energy is considered.

제안 방법

In order to evaluate the effect of change in thickness of CFRP, the cross-section of the circular concrete bridge pier were to set to a fixed dimension and the height of the CFRP were set to height of ¼ of the column.
In this study, numerical models were subjected to gravity loading and dynamic loading were applied until failure of the structure. Fig.
The simulated structure was analyzed under three (3) model cases, the initial case, the change in height of CFRP (length-to-height ratio or wrapping height), and the change in thickness of CFRP (width-to-span ratio or relative wrapping thickness). In order to account for the effect of change in height of CFRP, the cross-section of the circular concrete bridge pier was constant and the thickness of the CFRP and set 2mm.
In order to increase this type of criteria, confinement or external strengthening of concrete column structures could be provided in order to increase the ductility criteria. Therefore, in this paper the seismic performance of the structure was evaluated using the calculated ductility. The progressive development of computer simulations was utilized using a finite element software, ABAQUS (2013), to numerically evaluate and observe the relationship of ductility of the structure with respect to length-to-height ratio and width-to-span ratio of CFRP.

데이터처리

The ductility of the structure was evaluated using numerical analysis. The elastic, inelastic and total energy were obtained through numerical integration.

이론/모형

Finite element program ABAQUS was chosen to simulate the model. The software has wide variety of modelling capability and has concrete damage plasticity (CDP) option that captures the real behavior of concrete.

성능/효과

(1) For the change of length-to-height ratio, it was found out that using CFRP as reinforcement with ratio of 0.25 to 1.0 could increase the ductility of the circular concrete column from 78 % ranging up to 89~92 %. In this regard, the continuous use of CFRP throughout the length of circular concrete structure showed significant improvement in the base shear, stress capacity, lateral deformation and ductility.
(2) The change of width-to-span ratio indicated that the increase in the thickness of CFRP also increases the ductility of the structure. It was found out that from the ductility of the original structure, 78 %, it could be improved ranging from 85 % up to 89 % with a wrapping thickness ratio of 0.
Table 8 lists the ductility of the structure according to change in wrapping ratio and relative thickness of the reinforcement. Based from the results, each of the specimen confined by CFRP reduced the risk in brittle failure, thus, improving the seismic performance of the structure. In particular, the increase of length-to-height ratio of the reinforcement significantly contributed to the enhancement of ductility of the structure than the increase of width-to-span.
Tables 6 and 7 present the base shear and deformation as the length-to-height ratio and width-to-span ratio varies. Based from the results, it was observed that the increase of thickness in CFRP is capable of slightly improving the performance of the structure but not as significant as change in length-to-height ratio.
(2) The change of width-to-span ratio indicated that the increase in the thickness of CFRP also increases the ductility of the structure. It was found out that from the ductility of the original structure, 78 %, it could be improved ranging from 85 % up to 89 % with a wrapping thickness ratio of 0.0025 to 0.0075. However, the effect of increasing the thickness of CFRP to the overall performance structure tends to be insignificant.

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